For many years, electric gas discharges have been used in a variety of applications including etching, deposition, sterilization, functionalization, etc. Commonly, these devices require sub-atmospheric pressures necessitating costly pressure locks and vacuum systems. Dielectric barrier discharge (DBD) systems, however, can operate at, below, or even above atmospheric pressure. Most DBD systems have been driven by continuous wave, radio frequency, power sources. In recent years, however, there has been increased use of pulsed power sources. In comparison with the RF DBD's, pulsed power DBD's, with their greater instantaneous powers, are able to achieve higher electron and reactive species densities together with higher electron energies leading to increased exposure dosage and decreased required processing time. In addition, the pulsed systems tend to be more stable and spatially uniform than the RF DBD's. Thus devices and techniques that lead to increases in power density without excessive gas heating, arcs, or narrow filamentary discharges are of considerable value. For reasons of economy we emphasize air or nitrogen as the working gases, although, glow-like discharges have been produced with this device in Nitrogen, Oxygen, sulfur hexafluoride (SF6), carbon tetrafluoride CF4), Helium, Neon, Argon, Krypton, acetylene, titanium tetrachloride (TiCL4), and mixtures of some of the previously mentioned gases. The highest instantaneous power densities in nitrogen as in a glow-like DBD have been reported by Golubovskii (˜2 kw/cm2). The highest value observed using techniques described in this application is around 100 kW/cm2.
As noted above, one useful application of plasma discharge systems is the use of the plasma for sterilization. U.S. patent application publication number US2004/0037736 A1 to Perruchot et al., which is hereby incorporated by reference, contains an extensive background treatment in the definition of sterilization and the various sterilization methods currently known and in use. As explained by Perruchot et al., the sterilization methods that use plasma discharge systems operate by creation of reactive species such as radicals of ionized and/or excited species. Various improvements on plasma discharge sterilization methods are further discussed in Perruchot.